Phalanx bone

{{Image frame|content= File:Phalanges of left foot - animation01.gif File:Phalanges of left foot - animation02.gif Toe bones, or phalanges of the foot. Note the big toe has no middle phalanx. People vary; sometimes the smallest toe also has none (not shown). The phalanges are the bones that make up the fingers of the hand and the toes of the foot. There are 56 phalanges in the human body, with fourteen on each hand and foot. Three phalanges are present on each finger and toe, with the exception of the thumb and big toe, which possess only two. The middle and far phalanges of the fifth toes are often fused together (symphalangism). The phalanges of the hand are commonly known as the finger bones. The phalanges of the foot differ from the hand in that they are often shorter and more compressed, especially in the proximal phalanges, those closest to the torso. A phalanx is named according to whether it is proximal, middle, or distal and its associated finger or toe. The proximal phalanges are those that are closest to the hand or foot. In the hand, the prominent, knobby ends of the phalanges are known as knuckles. The proximal phalanges join with the metacarpals of the hand or metatarsals of the foot at the metacarpophalangeal joint or metatarsophalangeal joint. The intermediate phalanx is not only intermediate in location, but usually also in size. The thumb and large toe do not have middle phalanges. The distal phalanges are the bones at the tips of the fingers or toes. The proximal, intermediate, and distal phalanges articulate with one another through interphalangeal joints of hand and interphalangeal joints of the foot. Bone anatomy Each phalanx consists of a central part, called the body, and two extremities. • The body is flat on either side, concave on the palmar surface, and convex on the dorsal surface. Its sides are marked with rough areas giving attachment to fibrous sheaths of flexor tendons. It tapers from above downwards. • The proximal extremities of the bones of the first row present oval, concave articular surfaces, broader from side to side than from front to back. The proximal extremity of each of the bones of the second and third rows presents a double concavity separated by a median ridge. The middle are remarkably small and short, but rather broader than the proximal. The distal phalanges, as compared with the distal phalanges of the finger, are smaller and are flattened from above downward; each presents a broad base for articulation with the corresponding bone of the second row, and an expanded distal extremity for the support of the nail and end of the toe. Distal phalanx In the hand, the distal phalanges are flat on their palmar surface, small, and with a roughened, elevated surface of horseshoe form on the palmar surface, supporting the finger pulp. The flat, wide expansions found at the tips of the distal phalanges are called "apical tufts". They support the fingertip pads and nails. The phalanx of the thumb has a pronounced insertion for the flexor pollicis longus (asymmetric towards the radial side), an ungual fossa, and a pair of unequal ungual spines (the ulnar being more prominent). This asymmetry is necessary to ensure that the thumb pulp is always facing the pulps of the other digits, an osteological configuration which provides the maximum contact surface with held objects. The flexor insertion is sided by two fossaethe ungual fossa distally and the proximopalmar fossa proximally. Development The number of phalanges in animals is often expressed as a "phalangeal formula" that indicates the numbers of phalanges in digits, beginning from the innermost medial or proximal. For example, humans have a 2/3/3/3/3 formula for the hand, meaning that the thumb has two phalanges, whilst the other fingers each have three. In the distal phalanges of the hand the centres for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the distal phalanges are the first to ossify. ==Function==

The distal phalanges of ungulates carry and shape nails and claws and these in primates are referred to as the ungual phalanges. ==History of phalanges==

Etymology Phalanx refers to an ancient Greek army formation in which soldiers stand side by side, several rows deep, like an arrangement of fingers or toes. Other animals Most land mammals, including humans, have a 2/3/3/3/3 formula in both the hands (or paws) and feet. Primitive reptiles usually had the formula 2/3/4/4/5, and this pattern, with some modification, remained in many later reptiles and in the mammal-like reptiles. The phalangeal formula in the flippers of cetaceans (marine mammals) varies widely due to hyperphalangy (the increase in number of phalanx bones in the digits). In humpback whales, for example, the phalangeal formula is 0/2/7/7/3; in pilot whales the formula is 1/10/7/2/1. In vertebrates, proximal phalanges have a similar placement in the corresponding limbs, be they paw, wing or fin. In many species, they are the longest and thickest phalanx ("finger" bone). The middle phalanx also has a corresponding place in their limbs, whether they be paw, wing, hoof or fin. The distal phalanges are cone-shaped in most mammals, including most primates, but relatively wide and flat in humans. Primates . In non-human, living primates the apical tufts vary in size, but they are never larger than in humans. Enlarged apical tufts, to the extent they actually reflect expanded digital pulps, may have played a significant role in enhancing friction between the hand and held objects during Neolithic toolmaking. Cetaceans Whales exhibit hyperphalangy. Hyperphalangy is an increase in the number of phalanges beyond the plesiomorphic mammal condition of three phalanges-per-digit. Hyperphalangy was present among extinct marine reptiles -- ichthyosaurs, plesiosaurs, and mosasaurs -- but not other marine mammals, leaving whales as the only marine mammals to develop this characteristic. The evolutionary process continued over time, and a very derived form of hyperphalangy, with six or more phalanges per digit, evolved convergently in rorqual whales and oceanic dolphins, and was likely associated with another wave of signaling within the interdigital tissues. The sloth spends its life hanging upside-down from branches, and has highly specialized third and fourth digits for the purpose. They have short and squat proximal phalanges with much longer terminal phalanges. They have vestigial second and fifth metacarpals, and their palm extends to the distal interphalangeal joints. The arboreal specialization of these terminal phalanges makes it impossible for the sloth to walk on the ground where the animal has to drag its body with its claws. ==Additional images==

File:Q11.jpg|Phalanges File:Carpus2.jpg|Phalanges File:Unilateral extra phalangeal crease.jpg|Unilateral extra phalangeal crease File:814 Radiograph of Hand.jpg|Joints of the hand in an X-ray image File:Finger phalanges movement.png|Movement of the three finger phalanges: distal, middle and proximal ==See also==